Ceramic body forming batch materials comprising silica methods using the same and ceramic bodies made therefrom

ABSTRACT

The disclosure relates to ceramic-body-forming batch materials comprising at least one pore former and inorganic batch components comprising at least one silica source having a specified particle size distribution, methods of making ceramic bodies using the same, and ceramic bodies made in accordance with said methods. The disclosure additionally relates to methods for reducing pore size variability in ceramic bodies and/or reducing process variability in making ceramic bodies.

FIELD OF THE DISCLOSURE

Disclosed herein are ceramic-body-forming batch materials comprising atleast one pore former and inorganic batch components comprising at leastone silica source having a specified particle size distribution. Thedisclosure further relates to methods of making ceramic bodies, saidmethods comprising, in part, forming a batch material comprising atleast one pore former and inorganic batch components comprising at leastone silica source having a specified particle size distribution andceramic bodies made in accordance with said methods. The disclosureadditionally relates to methods for reducing pore size variability inceramic bodies and/or reducing process variability in making ceramicbodies.

BACKGROUND

Ceramic bodies, such as aluminum titanate and cordierite ceramics, maybe used in a variety of applications. For example, such bodies areviable for use in the severe conditions of exhaust gas environments,including, for example as catalytic converters and as diesel particulatefilters. Among the many pollutants in the exhaust gases filtered inthese applications are, for example, hydrocarbons and oxygen-containingcompounds, the latter including, for example, nitrogen oxides (NOx) andcarbon monoxide (CO), and carbon based soot and particulate matter.

Ceramic bodies exhibit high thermal shock resistance, enabling them toendure the wide temperature variations encountered in their application,and they also exhibit other advantageous properties for dieselparticulate filter applications, such as, for example, high porosity,low coefficient of thermal expansion (CTE), resistance to ash reaction,and a modulus of rupture (MOR) adequate for the intended application.

With engine management schemes becoming more and more sophisticated, andwith catalyst compositions ever changing, there exists a need for theability to vary or tailor the properties of these ceramic bodies, forexample their pore size, porosity, pore size distribution, andmicrostructure. Moreover, there is a need for methods to make ceramicbodies having these desirable properties. Additionally, there is a needfor methods to reduce pore size variability in ceramic bodies and/orreduce process variability in making ceramic bodies.

While pore formers may be selected to produce a range of porosity and/orpore size in a ceramic body based on their shape and size, they may beexpensive and can make extrusion and drying difficult, including oftenrequiring complicated firing cycles to burn out the pore former withoutcracking the underlying parts.

The inventors have now discovered novel ceramic-body-forming batchmaterials, ceramic bodies, and methods of making the same that may allowfor the ability to vary or tailor the properties of these ceramicbodies, for example their pore size, porosity, pore size distribution,and microstructure.

SUMMARY

In accordance with the detailed description and various exemplaryembodiments described herein, the disclosure relates to novelceramic-body-forming batch materials comprising (a) at least one poreformer, and (b) inorganic batch components comprising at least onesilica source having a specified particle size distribution. In variousembodiments, the silica source may have a particle size distributionwith an sD_(breadth) (i.e. (sd₉₀−sd₁₀)/sd₅₀) of about 2 or less and amedian particle size (sd₅₀) ranging from about 5 μm to 240 μm.

The disclosure further related to methods of making ceramic bodies, saidmethods comprising forming a batch material comprising at least one poreformer and inorganic batch components comprising at least one silicasource; forming a green body from said batch material; and firing thegreen body to obtain the ceramic body. In various embodiments, thesilica source may have a particle size distribution with an sD_(breadth)of about 2 or less and a median particle size (sd₅₀) ranging from about5 μm to 240 μm. The disclosure also relates to ceramic bodies made inaccordance with these methods.

The disclosure also relates to methods for reducing pore sizevariability in ceramic bodies and/or reducing process variability inmaking ceramic bodies, the method comprising, in part, reducing thevariability in the particle size distribution of a first lot of a silicasource which comprises an inorganic batch component in a first batchrelative to a second lot of a silica source which comprises an inorganicbatch component in a second batch. In various embodiments the first lotsilica source has a particle size distribution with an sD_(breadth) ofabout 2 or less, and a median particle size (sd₅₀) ranging from about 5μm to 240 μm. Additionally, in further embodiments, the median particlesize (sd₅₀) of the silica source may vary by about ±4 μm or less, thesd₁₀ may vary by about ±0.5 μm or less, and the sd₉₀ may vary by about±10 μm or less.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention as claimed and are incorporated in andconstitute a part of this specification. The drawings are not intendedto be restrictive, but rather illustrate exemplary embodiments and,together with the description, serve to explain the principles of theinvention as claimed.

FIG. 1 depicts the properties of ceramic bodies obtained according toone embodiment as described in Example 1; and

FIG. 2 depicts the particle size distribution of silica sourcesdescribed in Examples 1 and 2.

DETAILED DESCRIPTION

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory only,and are not restrictive of the claimed invention. Other embodiments willbe apparent to those skilled in the art from consideration of thespecification disclosed herein. It is intended that the specificationand examples be considered as exemplary only.

As used herein, the use of “the,” “a,” or “an” means “at least one,” andshould not be limited to “only one” unless explicitly indicated to thecontrary. Thus, for example, the use of “the silica source” or “a silicasource” is intended to mean “at least one silica source.”

The disclosure relates to ceramic-body-forming batch materialscomprising at least one pore former, and inorganic batch componentscomprising at least one silica source.

As used herein, the terms “ceramic-body-forming batch material,” “batchmaterial,” and variations thereof, are intended to mean a substantiallyhomogeneous mixture comprising (a) at least one pore former and (b)inorganic batch components. The batch material of the present disclosuremay be used to make ceramic bodies, including, but are not limited to,those comprised of cordierite, aluminum titanate composites, mullite,alkali and alkaline-earth feldspar phases, and silicon carbide.

The inorganic batch components comprise at least one silica source.Sources of silica include, but are not limited to, non-crystallinesilica, such as fused silica or sol-gel silica, colloidal silica,silicone resin, low-alumina substantially alkali-free zeolite,diatomaceous silica, and crystalline silica, such as quartz orcristobalite. Additionally, the sources of silica may includesilica-forming sources that comprise a compound that forms free silicawhen heated, for example, silicic acid or a silicon organometalliccompound.

In various embodiments, the silica source may have a median particlesize (sd₅₀) ranging from about 5 μm to 240 μm, for example from about 5μm to 50 μm, 10 μm to 40 μm or from about 15 μm to 35 μm.

In various embodiments, the silica source may have a particle sizedistribution with an sD_(breadth) (i.e. (sd₉₀−sd₁₀)/sd₅₀) of about 2 orless, for example about 1.7 or less, or 1.4 or less.

It is within the ability of one skilled in the art to select the amountof silica source such that the desired ceramic body may be formed. Invarious exemplary embodiments, the silica source may comprise from about5 wt % to about 60 wt % of the inorganic batch material on an oxidebasis, such as about 5 wt % to about 20 wt %, or about 8 wt % to about12 wt %.

In further embodiments, the inorganic components may further comprisecomponents for forming various ceramic bodies, including, but notlimited to, at least one alumina source, at least one titania source, atleast one magnesium source; at least one strontium source, and at leastone calcium source. In various embodiments, the inorganic components maybe chosen such that the batch material may form at least one of siliconcarbide, aluminum titanate composite, mullite, alkali feldspar phases,or cordierite ceramic body. In at least one embodiment, the batchmaterial may form an aluminum titanate composite or cordierite ceramicbody.

The ceramic-forming-batch material of the disclosure further comprises apore former. As used herein, the terms “pore former,” “pore-formingmaterial,” and variations thereof, mean materials selected from thegroup comprising: carbon (e.g., graphite (natural or synthetic),activated carbon, petroleum coke, and carbon black), starch (e.g., corn,barley, bean, potato, rice, tapioca, pea, sago palm, wheat, canna, andwalnut shell flour), and polymers (e.g., polybutylene,polymethylpentene, polyethylene (preferably beads), polypropylene(preferably beads), polystyrene, polyamides (nylons), epoxies, ABS,Acrylics, and polyesters (PET)). In at least one embodiment, the poreformer may be chosen from starches. By way of example only, the poreformer may be a starch chosen from potato and pea starch.

Non-limiting examples of pore formers include Native Potato Starchmarketed by Emsland Starke GmbH from Kyrita and Emlichheim, Germanyfacilities and Native Pea Starch marketed by Emsland Starke GmbH fromthe Emlichheim, Germany facility.

In various exemplary embodiments, one of skill in the art may choose thepore former such that the median particle size (pd₅₀) may range fromabout 1 μm to 400 μm, such as, for example, from about 5 μm to 300 μm,from about 5 μm to 200 μm, from about 5 μm to 100, or from about 5 μm to60 μm.

In various embodiments of the disclosure, the pore former may have amedian particle size (pd₅₀), wherein the ratio of sd₅₀ to pd₅₀ is in therange of from about 0.6 to about 1.5, such as, for example from about0.8 to 1.3.

In various embodiments of the disclosure, selecting a pore former andsilica source within these ranges may result in ceramic bodies havingmore narrow pore size distribution and/or enhanced physical properties(e.g., strength, pressure drop, and coefficient of thermal expansion(CTE)) than ceramic bodies made with components outside the scope ofthis ratio.

In various exemplary embodiments, the pore former may be chosen to bepresent in any amount to achieve a desired result. For example, the poreformer may comprise at least 1 wt % of the batch material, added as asuper-addition (i.e., the inorganic components comprise 100% of thebatch material, such that the total batch material is 101%). Forexample, the pore former may comprise at least 5 wt %, at least 10 wt %,at least 15 wt %, at least 20 wt %, at least 30 wt %, at least 40 wt %,or at least 50 wt % of the batch material, added as a super-addition. Infurther embodiments, the pore former may comprise less than 20 wt % ofthe batch material as a super-addition.

In various embodiments of the disclosure, the batch material may bemixed with any other known component useful for making batch material.For example, the batch material may further comprise at least oneorganic binder. In such an embodiment, it is within the ability of oneskilled in the art to select an appropriate binder. By way of exampleonly, an organic binder may be chosen from cellulose-containingcomponents, such as, for example, methylcellulose, methylcellulosederivatives, and combinations thereof.

It is also within the ability of one skilled in the art to select anappropriate solvent, if desired. In various exemplary embodiments, thesolvent may be water, for example deionized water.

In additional exemplary embodiments, the batch material may be mixedwith any other known component useful for making batch material, suchas, for example, at least one lubricant.

The disclosure further relates to methods of making a ceramic body usingbatch materials of the disclosure, wherein said methods may comprise:preparing a batch material; forming a green body from said batchmaterial; and firing the green body to obtain a ceramic body.

The ceramic-body-forming batch material may be prepared by any methodknown to those of skill in the art. By way of example, in at least oneembodiment, the inorganic components may be combined as powderedmaterials and intimately mixed to form a substantially homogeneousmixture. The pore former may be added to form a batch mixture before orafter the inorganic components are intimately mixed. In variousembodiments, the pore former and inorganic components may then beintimately mixed to form a substantially homogeneous batch material. Itis within the ability of one of skill in the art to determine theappropriate steps and conditions for combing the inorganic materials andpore former to achieve a substantially homogeneous batch material.

The additional components, such as lubricant, organic binder, andsolvent, may be mixed with the batch material individually, in anyorder, or together to form a substantially homogeneous mixture. It iswithin the ability of one of skill in the art to determine theappropriate conditions for mixing the batch material with the additionalcomponents, such as organic binder and solvent, to achieve asubstantially homogeneous material. For example, the components may bemixed by a kneading process to form a substantially homogeneous mixture.

The mixture may, in various embodiments, be formed into a ceramic bodyby any process known to those of skill in the art. By way of example,the mixture may be injection molded or extruded and optionally dried byconventional methods known to those of skill in the art to form a greenbody.

In various exemplary embodiments, the green body may then be fired toform a ceramic body. It is within the ability of one skilled in the artto determine the appropriate method and conditions for firing a ceramicbody, such as, for example, firing conditions including equipment,temperature, and duration, to achieve a ceramic body, depending in partupon the size and composition of the green body.

The disclosure further relates to the ceramic bodies made in accordancewith the methods of the disclosure. In various exemplary embodiments,the ceramic body may be a silicon carbide, aluminum titanate composite,or cordierite ceramic body.

In at least one embodiment, the ceramic bodies may have a porosity inthe range of from about 40% to about 70%, for example about 40% to 60%,or 40% to 50%.

In further embodiments, the ceramic bodies may have a pore sizedistribution with a D_(breadth) (i.e. (d₉₀−d₁₀)/d₅₀) less than about0.70 for example less than about 0.60, less than about 0.50, less thanabout 0.45, such as less than about 0.41

The disclosure also relates to methods for reducing pore sizevariability in ceramic bodies and/or reducing process variability inmaking ceramic bodies. As used herein, the term “reducing pore sizevariability,” and variations thereof, is intended to mean that relativeto a control or standard ceramic body, there is less variation in poresize parameters (median pore size (d₅₀) and/or pore size distribution ascharacterized by the D_(breadth) or D_(factor)) of a ceramic body madein accordance with the inventive method as compared to the variation inpore size characteristics of a ceramic body not made in accordance withthe inventive method. As used herein, the term “reducing processvariability,” and variations thereof, is intended to mean that relativeto specification or control process parameters, such as firing cycles,there is less variation in process parameters for the methods of thedisclosure as compared to methods outside the scope of the disclosure.

In various embodiments, these methods comprise reducing the variabilityin the particle size distribution of at least one silica sourcecomprising an inorganic batch component. As used herein, the term“reducing the variability in the particle size distribution” is intendedto mean that various particle size parameters characterizing thematerial vary less from the standard or specifications for that materialthan is conventionally used. For example, in various embodiments of thedisclosure, the median particle size of the silica source (sd₅₀) mayvary by about ±4 μm or less, such as about ±2 μm or less or about ±1 μmor less. In other embodiments, the particle size sd₁₀ of the silicasource may vary by about ±0.5 μm or less, such as about ±0.25 μm or lessor about ±0.125 μm or less. And, in other embodiments, the particle sizesd₉₀ of the silica source may vary by about ±10 μm or less, such asabout ±5 μm or less or about ±2.5 μm or less.

The silica source for use in these methods is the same as that describedabove. For example, in various embodiments, the silica source may have aparticle size distribution with an sD_(breadth) of about 2 or less, anda median particle size (sd₅₀) ranging from about 5 μm to 240 μm.

In various embodiments, the ceramic body made in accordance with thismethod may be an aluminum titanate composite ceramic body or acordierite ceramic body.

When fired, the silica source reacts into the matrix, leaving holes orpores in the ceramic body. The shape and size of these holes may beidentical to the shape and size of the silica particles that createdthem.

By carefully selecting the particle size distribution of the silicasource, one may tailor the properties of the ceramic body, e.g., poresize distribution, and/or improve properties. In various embodiments,selecting a silica source with a narrow particle size distribution mayresult in a ceramic body with increased strength and a reducedcoefficient of thermal expansion. In other embodiments, reducing thefine silica particles in the silica source, e.g., increasing theparticle size sd₁₀, may reduce shrinkage variability. In otherembodiments, reducing the large silica particles in the silica source,e.g., decreasing the particle size sd₉₀, may improve filtrationefficiency of the resulting ceramic body.

Unless otherwise indicated, all numbers used in the specification andclaims are to be understood as being modified in all instances by theterm “about,” whether or not so stated. It should also be understoodthat the precise numerical values used in the specification and claimsform additional embodiments. Efforts have been made to ensure theaccuracy of the numerical values disclosed in the Examples. Any measurednumerical value, however, can inherently contain certain errorsresulting from the standard deviation found in its respective measuringtechnique.

Other embodiments will be apparent to those skilled in the art fromconsideration of the specification. It is intended that thespecification and examples be considered as exemplary only, with a truescope and spirit of the invention being indicated by the claims.

EXAMPLES Example 1

Three aluminum titanate composite ceramic bodies were prepared using thesame batch materials and amounts, but for the use of two differentsilica sources. Specifically, batch A was prepared using inorganicmaterials comprising 49.67 wt % alumina, 30.33 wt % titania, 10.31 wt %silica “A” (comparative), 8.10 wt % strontium carbonate, 1.39 wt %calcium carbonate, and 0.20 wt % lanthanum oxide. Batches B and C wereprepared using the same materials and amounts but for the use of adifferent silica source, silica “B”. Particle size data for the twosilica sources are set forth in Table 1 below. Additionally, FIG. 2 alsoshows the particle size distribution for the two silica sources used inthe batches.

For both batches, the inorganic materials were combined with one anotherin powder form. Then pore-forming materials (3.50 wt % 4566 graphite and9.0 wt % pea starch, as super-additions) were added to the inorganicmaterials and intimately mixed to produce a substantially homogeneousmixture.

Methylcellulose, which comprised 4.5 wt % of the mixtures as asuper-addition, was added as a powder to the batch materials. Thenwater, which comprised 16 wt % of the mixture as a super-addition, wasadded to form a wet mixture.

The plasticized mixtures were extruded to make cellular ware (e.g., 300cells per square inch (cpsi)/10 mil web thickness), and the resultinggreen bodies were fired on a standard alumina titanate firing scheduleas described in International Publication No. WO 2006/130759, which isincorporated herein by reference.

The resulting alumina titanate composite ceramic bodies were analyzed.Their properties are set forth in Table 2 below. Additionally, FIG. 1 isa plot of pore size diameter (μm) on the x-axis versus log differentialintrusion (ml/g) on the y-axis.

As seen in Table 2 and FIG. 1, the ceramic body formed from Batch A,which is not within the scope of the disclosure, has a greaterD_(breadth), i.e., a greater percentage of fine pores, than the bodiesformed from Batches B and C, which are within the scope of thedisclosure. Thus, the ceramic bodies formed from Batches B and C mayexhibit improved filtration efficiency.

Batch A has higher coefficients of thermal expansion at 800° C. and 1000than Batches B and C, indicating that Batches B and C have lessshrinkage. Additionally, Batch A has a lower modulus of rupture, thanBatches B and C, indicating that Batches B and C result in strongerceramic bodies.

TABLE 1 Particle Sizes of Silica Sources sd10 sd50 sd90 Type (μm) (μm)(μm) A 4 25 63 B 15 29 57

TABLE 2 Properties of Ceramic Bodies (Batches A-C) Properties of CeramicBody Po- CTE (at CTE (at ros- d50 d10 d90 800° 1000° MOR Batch ity (μm)(μm) (μm) D_(breadth) C.) C.) (psi) A 45.34 13.72 9.51 20.64 0.81 0.95.4 201 B 45.49 14.92 10.80 19.67 0.59 −0.5 4.1 227 C 45.10 15.20 11.3321.32 0.66 −1.1 4.4 222

Example 2

Batch material for making aluminum titanate composite ceramic bodies wasprepared. Specifically, the batch was prepared using inorganic materialscomprising 59.11 wt % alumina, 30.66 wt % titania, 8.27 wt % silica “B”,1.96 wt % yittrium oxide. Particle size data for the silica source isset forth in Table 1 above.

The inorganic materials were combined with one another in powder form.Then pore-forming material (12.0 wt % pea starch, as a super-addition)was added to the inorganic materials and intimately mixed to produce asubstantially homogeneous mixture.

Methylcellulose, which comprised 4.5 wt % of the mixture as asuper-addition, was added as a powder to the batch materials. Thenwater, which comprised 14 wt % of the mixture as a super-addition, wasadded to form a wet mixture.

The plasticized mixture was extruded to make cellular ware (e.g., 300cells per square inch (cpsi)/14 mil web thickness). Three resultinggreen bodies were fired in an electric kiln in air and at a 60° C./hourheating rate to 1400° C., 1420° C., and 1440° C., for samples D, E, andF, respectively, with a 16 hour hold time. The bodies were then cooledat 300° C./hour.

The resulting alumina titanate composite ceramic bodies were analyzed.Their properties are set forth in Table 3 below.

As seen in Table 3, the ceramic bodies have a low D_(factor) andD_(breadth) i.e., a narrow range of pore size and low percentage of finepores. Thus, the ceramic bodies may exhibit good improved filtrationefficiency.

Additionally, the batches have low coefficients of thermal expansion at1000° C., indicating that they have low shrinkage.

TABLE 3 Properties of Ceramic Bodies (Samples D-F) Properties of CeramicBody Porosity d50 d10 d90 CTE Sample (%) (μm) (μm) (μm) D_(breadth)D_(factor) (at 1000° C.) D 41.7 10.5 7.9 12.6 0.45 0.25 3.9 E 41.2 10.98.3 12.7 0.41 0.23 2.7 F 40.3 11.3 8.7 13.5 0.42 0.23 1.1

1-20. (canceled)
 21. A method of making a ceramic body, said methodcomprising: preparing a batch material comprising: at least one poreformer, and inorganic batch components comprising: at least one silicasource; and (ii) at least one source chosen from alumina sources,titania sources, magnesium sources, strontium sources, and calciumsources; forming a green body from said batch material; and firing thegreen body to obtain a ceramic body; wherein the at least one silicasource has a particle size distribution with an sD_(breadth) of about 2or less, and a median particle size (sd₅₀) ranging from about 5 μm to240 μm.
 22. The method of claim 21, wherein the particle sizedistribution sD_(breadth) of the at least one silica source is about 1.7or less.
 23. The method of claim 21, wherein the particle sizedistribution sD_(breadth) of the at least one silica source is about 1.4or less.
 24. The method of claim 21, wherein the median particle size(sd₅₀) of the at least one silica source ranges from about 5 μm to 50μm.
 25. The method of claim 21, wherein the median particle size (sd₅₀)of the at least one silica source ranges from about 10 μm to 40 μm. 26.The method of claim 21, wherein the median particle size (sd₅₀) of theat least one silica source ranges from about 15 μm to 35 μm.
 27. Themethod of claim 21, wherein said at least one pore former has a medianparticle size (pd₅₀), and the ratio of sd₅₀ to pd₅₀ is in the range offrom about 0.6 to about 1.5.
 28. The method of claim 21, wherein said atleast one pore former has a median particle size (pd₅₀), and the ratioof sd₅₀ to pd₅₀ is in the range of from about 0.8 to about 1.3.
 29. Themethod of claim 21, wherein the inorganic batch components are chosen soas to form an aluminum titanate composite ceramic-body-forming batchmaterial or a cordierite ceramic-body-forming batch material.
 30. Aceramic body made in accordance with a method comprising: preparing abatch material comprising: at least one pore former, and inorganic batchcomponents comprising: (iii) at least one silica source; and (iv) atleast one source chosen from alumina sources, titania sources, magnesiumsources, strontium sources, and calcium sources; forming a green bodyfrom said batch material; and firing the green body to obtain a ceramicbody; wherein the at least one silica source has a particle sizedistribution with an sD_(breadth) of about 2 or less, and a medianparticle size (sd₅₀) ranging from about 5 μm to 240 μm.
 31. A ceramicbody prepared according to claim 30, wherein the ceramic body has aporosity in the range of from about 40% to about 70%, and a pore sizedistribution with a D_(breadth) of less than about 0.70.